It is well known that as the cost of crude oil increases, numerous efforts have been made to find and develop alternative fuels, particularly fuels that have a renewable, rather than a limited, source. Considerable effort has been expended researching potential fuels from regenerable biological sources, or biofuels. Biodiesel is a diesel fuel-equivalent, processed fuel derived from biological sources (such as vegetable oils), which may be used in unmodified diesel engine vehicles.
In the context herein, biodiesel fuels include, but are not necessarily limited to, alkyl esters of a fatty acid, typically either the ethyl ester or methyl ester of a fatty acid. Thus, many biodiesel fuels may be understood to contain fatty acid methyl esters (FAME). Most biodiesel fuel is presently made by transesterification of fatty acids. Biodiesel fuel may also be made from free fatty acids using an acid catalyst. There are other processes that use an ion-exchange resin catalyst. Most biodiesel fuels are made from vegetable oils, including, but not necessarily limited to rapeseed, soybean, cotton seed, corn, jotropha and the like oils. Some biodiesel is made from animal fats, including, but not limited to beef and pig tallow, chicken fat, fry grease, restaurant trap grease, fish oil, and the like. Efforts are also being made to blend FAME compounds to modify properties such as low temperature handling, for instance esters from palm and soybean oils or soybean and tallow oils (e.g. beef). The mixtures may be complex. All of these fall within the definition of biodiesel fuel herein. Non-esterified or straight vegetable oils (SVO) or straight waste vegetable oil (WVO) is not included in the definition of biodiesel fuels herein. However, biodiesel fuels as defined herein may include these non-esterified SVOs or WVOs in minor proportions (less than 50 volume %, and in another embodiment less than about 1%).
The biodiesel fuel B100 has a particular definition, including, among other parameters, a minimum ester content of 96.5 wt %. It may be made by transesterifying triglycerides from palm oil, soybean oil, tallow, rapeseed oil and/or waste oils with methanol in the presence of a catalyst.
Depending on the particular synthesis process, biodiesel fuels may contain acidic components or impurities, typically free fatty acids (FFA). These and other acid components in fuels are undesirable due to corrosivity concerns, oxidative stability and other problems. The acidity of the acid impurities in biodiesel fuels may be measured as an acid number or total acid number (TAN), which is defined as the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of the fuel.
There is a need to reduce TAN in biodiesel fuels. It is desirable to discover a method and/or composition for reducing the true acidic potential, as represented by total acid number (TAN), of biodiesel fuel. The acidic potential may be defined herein as the ability or tendency to form acidic species in subsequent storage, transport, or processing of the biodiesel fuel.